1. Field of the Invention
This invention generally relates to a multi-layer plastic pipe and a method for manufacturing the same, and, in particular, to such a plastic pipe as a duct for use as an automobile component like an intake manifold.
2. Description of the Prior Art
Since the advent of a method for manufacturing a plastic pipe whose center axis varies two-dimensionally or three-dimensionally in an arbitrary manner by blow molding, many of the pipes or ducts used in automobiles have been and still are being replaced with plastic pipes and ducts. By providing such plastic pipes having a two-dimensional or three-dimensional arbitrary shape, for example, when ducts or pipes are to be disposed in a limited space of an automobile, such as an engine room, without the necessity to assemble a plurality of pipe components having simpler shapes, a plastic pipe of a unitary structure having a complicatedly bent shape, either two-dimensionally or three-dimensionally, can be provided, which contributes to facilitate a mounting operation of ducts or pipes. In addition, with such a plastic pipe of a unitary structure, since there is no connection between pipe components, there is no possibility of occurrence of leaks of a fluid passing through the ducts or pipes. For this reason, many of the conventional ducts or pipes made of rubber or the like for use in an engine room of an automobile have been and are being replaced by plastic pipes.
However, for example, even for duct and pipes for use in an engine room of an automobile, the required conditions may vary radically depending on the conditions in which they are used. In particular, since such a duct or pipe as an intake manifold is directly mounted on an engine, it is exposed to a significantly high temperature, and, moreover, since a vibration is directly applied thereto, a high degree of durability is required. For such a reason, the conventional intake manifold of an automobile was normally fabricated from a metal, such as aluminum. However, when a duct or pipe is to be manufactured from a metal, its manufacturing operation is complicated, difficult and expensive, and, moreover, the shape of a duct or pipe to be manufactured tends to be limited.
Therefore, a considerable effort and a sizable amount of money have been expended to try to replace such a duct or pipe as an intake manifold with a plastic duct or pipe; however, since it is a kind of duct or pipe which requires a high degree of heat-resistant characteristic as well as an increased durability, there has not yet been proposed any such plastic pipe or duct which can be put to practical use and its manufacturing method.
In accordance with the present invention, there is provided a multi-layered plastic pipe having a structure which provides a plastic pipe having a high degree of durability and heat-resistant characteristic and its manufacturing method. It is to be noted that here the terms xe2x80x9cpipexe2x80x9d and xe2x80x9cductxe2x80x9d are used interchangeably without changing their meanings.
In accordance with one aspect of the present invention, a multi-layered plastic pipe includes a hollow member formed in a desired shape from a first plastic material. At least one spacer member or projection formed from a second plastic material is provided at a predetermined location on an outer surface of the hollow member. In addition, an outer layer of a third plastic material is formed on the outer surface of the hollow member integrally with the spacer member.
In a preferred embodiment, the hollow member is manufactured to a desired shape by blow molding, and the spacer member is integrally formed with the hollow member when blow molded. Moreover, preferably, the outer layer includes at least one integrally formed flange portion at an end of the plastic pipe.
In accordance with another aspect of the present invention, a method for manufacturing a multi-layered plastic pipe by integrally forming an outer layer of a third plastic material on the outer peripheral surface of a hollow core which has been molded to a desired shape from a first plastic material. In accordance with a preferred method of the present invention, when the hollow core is placed in a mold cavity, at least one spacer member is interposed between the outer surface of the hollow core and the surface of the mold cavity to thereby define a predetermined gap therebetween. Then, the third plastic material in a molten state is injected into the cavity or the gap between the outer surface of the hollow core and the mold surface and the third plastic material thus injected is hardened, for example, by cooling, thereby forming an outer layer integrally on the outer surface of the hollow core, together with the spacer member. Preferably, the hollow core is fabricated by blow molding, together with the spacer member integrally. In this manner, since the spacer member is present between the hollow core and the cavity surface when the hollow core is placed in position in the mold cavity, a predetermined gap can be maintained between the hollow core and the cavity surface while the molten third plastic material is injected into the cavity. As a result, there can be formed an outer layer having a desired thickness and a desired shape across the entire surface of the hollow core.
In accordance with a further aspect of the present invention, there is provided another method for manufacturing a multi-layered plastic pipe. In accordance with this method, a plurality of mold segments are put together to define a mold cavity with a hollow plastic core placed inside the mold cavity. In this case, the mold segments are not completely put together, but a predetermined clearance is maintained between at least two of the mold segments such that the clearance may allow air to pass therethrough, but it does not allow any molten plastic material to pass therethrough. Under the condition, a plastic material in a molten state is supplied under pressure into the cavity, and, then, the mold segments are put together completely to thereby apply a pressure to the plastic material thus supplied into the cavity, so that an outer layer having a desired shape is integrally formed from a third plastic material on the outer peripheral surface of the hollow core in a unitary structure.
Preferably, in order to prevent the hollow core from being undesirably deformed during manufacture, the hollow plastic core may be filled with particles, such as sand, or a pressurized gas may be supplied into the interior of the hollow core at least while an external pressure is applied to the outer surface of the hollow core.
It is therefore a primary object of the present invention to provide an improved plastic pipe and a method for manufacturing the same.
Another object of the present invention is to provide a multi-layered plastic pipe having an increased durability and an enhanced heat-resistant characteristic and its manufacturing method.
A further object of the present invention is to provide an improved plastic pipe which can be used as an intake manifold and its manufacturing method.
A still further object of the present invention is to provide an improved plastic pipe simple in structure and thus easy to manufacture and low at cost.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.